The present invention relates to an image display apparatus of a video RAM system in which one picture plane of display means such as a CRT or the like is divided and a plurality of images are simultaneously displayed on those divided picture planes.
Generally, medical images, for instance, images which are obtained by observing the affected part in the body cavity of a human body by an endoscope and photographing the affected part, or the like are converted to electrical signals and are further stored in a memory medium of a large capacity such as an optical disk, magnetic disk or the like, thereby constituting an image file apparatus. A desired image is picked up from among the images stored in such an image file apparatus and is displayed on the display apparatus, thereby making use of it as one means for diagnosis.
In display of such medical images on the display apparatus, in order to realize easy comparison and diagnosis of the affected part, it is required to simultaneously display on the same screen a plurality of images such as, for example, (about twenty) images photographed in a single diagnosis for one patient by the endoscope, images photographed in the past by the endoscope for the same patient, images photographed with respect to the same portion of other patients who have the same disease, or the like.
Hitherto, as image display means for displaying a plurality of images on the same screen, for example, as shown in the Official Gazette of Japanese Patent Application Publication Laid-Open No. 12769/1979, image display means using a storage tube has been known. In this image display means, a plurality of images are recorded at different locations on the storage tube and the whole surface of the storage tube is scanned by an electron beam upon reproduction to read out signals, thereby allowing a plurality of images to be displayed.
However, the display means using such a storage tube has drawbacks such that images cannot be accurately displayed since there are not only restrictions in resolutions but also distortions upon recording and reproduction, and also the apparatus increases in size. Further, there are also drawbacks such that the display locations of the images which have been once stored and recorded in the storage tube cannot be changed upon reproduction and it is also difficult to change the images by newly storing image information, and the like.
As another conventional example, the image display means for transferring image data from a CPU to a display apparatus having a frame memory and allowing a plurality of images to be displayed on this display apparatus has been also known. However, in this display means, only one frame memory in which a plurality of images are stored is provided; therefore, to change the display locations of the images, the image data of as much as one screen has to be retransferred from the CPU, so that there is a drawback such that the display image cannot be easily changed.